1. Field of the Invention
The present invention relates to an anti-lock control system and, more particularly, to an anti-lock control system designed such that a value corresponding to a friction coefficient of a road surface on which a vehicle travels can be obtained, to enable an anti-lock control corresponding to the friction coefficient of the road surface.
2. Description of the Prior Art
An anti-lock control system is conventionally known from Japanese Patent Application Laid-Open No. 44039/80, which is designed, such that, the magnitude of friction coefficient of a road surface on which a vehicle travels is judged by the magnitude of a peak value of an acceleration in the course of restoring wheel speed to vehicle speed. An anti-lock control system is also conventionally known from Japanese Patent Application Laid-Open No. 155161/87, which is designed, such that, the magnitude of friction coefficient of a road surface on which a vehicle travels is judged by the magnitude of a restoring time between two speed points in the course of restoring of the wheel speed to a vehicle speed.
However, in the anti-lock control system disclosed in Japanese Patent Application Laid-Open No. 44039/80, the magnitude of friction coefficient is judged by measuring an acceleration at a pin point, and in the antilock control system disclosed in Japanese Patent Application Laid-Open No. 155161/87, a span between the measuring times is short. Therefore, in both such prior art anti-lock control systems, the judgement of the magnitude of friction coefficient is governed by an instantaneous behavior of the wheel. For this reason, it is difficult to judge the magnitude of friction coefficient, when the variations in wheel speed V.sub.w with respect to the vehicle speed V.sub.BL during travelling of the vehicle on a road surface of a low friction coefficient and the vehicle speed V.sub.BH during travelling of the vehicle on a road surface of a high friction coefficient are substantially equal.